Adding three vectors, why is this not right?

[rickbusiness]

http://postimage.org/image/gcb728073/

A=47.2 at 54.3deg above the x axis, B= 23.5 at 34.4 above the -x axis, C=30.5 along the -y axis.

A+B+C=(A_x+B_x+C_x)+(A_y+B_y+C_y) = R


R=√(R_x²+R_y²) = 22.63

θ=tan^-1R_y/R_x = 68.9deg


I just thought of the possibility that c may be at 90 deg instead of 270. As in pointing upwards along the neg y axis. Is there something i missed?

 

[PhanthomJay]

What values and signs are you getting for the x and y components of the three vectors? C points down with a magnitude of 30.5.

 

[rickbusiness]

A_x=Acosθ=47.2cos(54.3) = 27.5

A_y=Asinθ=47.2sin(54.3) = 38.3

B_x=Bcosθ=23.5cos(180-34.4) = -19.4

B_y=Bsinθ=23.5sin(180-34.4)= 13.3

C_x=Ccosθ=30.5cos(270)=0

C_y=Csinθ=30.5sin(270)=-30.5

R_x= 27.5-19.4+0=8.1
R_y=38.3+13.3-30.5=21.1R=√(8.1²)+(21.1²)=22.6

θ=tan^-1(21.1/8.1)=68.9deg

Ive tried rounding to different numbers of decimal places and not rounding till the end but I still had no success and I don't know why.

 

[Dick]

A_x=Acosθ=47.2cos(54.3) = 27.5

A_y=Asinθ=47.2sin(54.3) = 38.3

B_x=Bcosθ=23.5cos(180-34.4) = -19.4

B_y=Bsinθ=23.5sin(180-34.4)= 13.3

C_x=Ccosθ=30.5cos(270)=0

C_y=Csinθ=30.5sin(270)=-30.5

R_x= 27.5-19.4+0=8.1
R_y=38.3+13.3-30.5=21.1


R=√(8.1²)+(21.1²)=22.6

θ=tan^-1(21.1/8.1)=68.9deg

Ive tried rounding to different numbers of decimal places and not rounding till the end but I still had no success and I don't know why.

The problem doesn't say to find A+B+C. It says to find A-B+C.

 

[rickbusiness]

hahaha thanks!